.triangle (@_) { //调用该api前先调用该选择器
  width: 0;
  height: 0;
}
.triangle (L,@c,@w){ //L代表方向 算是一个匹配
  border-style: dashed dashed solid dashed;
  border: @w solid;
  border-color: transparent @c transparent transparent;
}
.triangle (R,@c,@w){
  width: 0;
  height: 0;
  border-style: dashed solid dashed  dashed;
  border: @w solid;
  border-color: transparent transparent  transparent @c;
}
.triangle (T,@c,@w){
  border-style:  solid dashed dashed  dashed;
  border: @w solid;
  border-color: @c transparent transparent transparent;
}
.triangle(B,@c,@w) {
    border-style: dashed dashed dashed solid ;
    border: @w solid;
    border-color: transparent transparent @c transparent;
}